JP2020518831A - Evaluation circuit, system and method for evaluating a capacitive sensor or an inductive sensor - Google Patents

Abstract

An evaluation circuit for evaluating a capacitive or inductive sensor is described. The evaluation circuit (1) comprises a first and second measurement connection (A, B) to which a sensor and/or a reference element (14, 15, 16) is connected, a first charge/discharge signal for a first measurement. A charging/discharging circuit (2) designed to output to the connection (A) and to output a second charging/discharging signal to the second measuring connection (B), a first charging/discharging signal and the second Comparator circuit (6) for comparing the temporal behavior of the charge and discharge signals of each other with each other, an integral connected to the output of the comparator circuit (6), and the output voltage of which changes according to the voltage at the output of the comparator circuit (6) A circuit (7). The output voltage of the integrator circuit (7) is connected to the first measuring connection (A) for adjusting the first charging/discharging signal or the second voltage for adjusting the second charging/discharging signal. Is connected to the measurement connection section (B). The measurement signal at the output (10) of the evaluation circuit (1) is derived from the output voltage of the integrator circuit (7), the measurement signal being the element at the first and second measurement connections (A, B). It is a measure of the impedance difference between (14,15,16). Systems for evaluating capacitive or inductive sensors and corresponding methods are also described.

Description

The present invention relates to an evaluation circuit for evaluating capacitive or inductive sensors, and corresponding systems and methods.

Capacitive or inductive sensors are used in many technical fields. Such sensors are typically used to identify the distance or position of the object being measured, or its change relative to the sensor. In this case it is used that the object to be measured has a feedback effect on the sensor or its elements. This feedback typically results in a measurable change in the impedance of the sensor or the sensor element of the sensor. For example, when a measured object of conductivity approaches an inductive sensor that operates on the eddy current principle, the magnetic field emitted from the sensor induces an eddy current in the measured object. Such eddy currents offset the changes in the magnetic field, which changes the inductance of the sensor coil and thus its impedance. When a non-conductive measured object approaches a capacitive sensor, it acts as a dielectric, thereby increasing the capacitance of the sensor. And this leads to a change in the impedance of the sensor. The same applies to other technologies for capacitive or inductive sensors.

Such impedance changes are usually not directly available. Instead, the change in impedance can be converted into a measurement signal by the evaluation circuit, which can then be further processed. The sensor element of the sensor is often added with a circuit element to form a parallel or series resonant circuit, and an AC voltage is applied to the resonant circuit. When the object to be measured approaches the range of influence of the sensor, the resonant circuit is detuned, which leads to a detectable phase shift between the resonant circuit signal and the excitation signal. The disadvantage in this case is that this introduces further dependencies, such as, for example, the dependency on the length of the connecting cable, the temperature dependency, and the tolerance of additional components. Furthermore, the components required to form the resonant circuit need to be placed close to the sensor, which is not possible in any application scenario.

Other evaluation circuits take the impedance of the two sensor elements of the sensor, or a differential approach in which one sensor element of the sensor is compared to a reference element. Such a circuit is known, for example, from EP 0166706 (A1). The oscillator alternately switches to the reference capacitor and the sensor capacitor by means of a switch. The control signal of the switch is formed by a frequency divider from the oscillation of the oscillator, the edges of which are conditioned by a Schmitt trigger. The control signal for the switch is converted into a differential signal by a conditioning circuit and output as a differential output signal of the circuit.

German Patent No. 3818371 (A1) discloses a differential inductive transmitter having two sensor coils, which can be added with a common capacitor to form an LC resonant circuit. The two sensor coils have a common connection which is connected to one of the two connections of the oscillator. A second connection of the oscillator is connected to a switch device, which alternately connects the oscillator to a second connection of one of the two sensor coils. One of the two sensor coils is thereby alternately excited and oscillates.

The disadvantage of these evaluation circuits is that switching elements are required, which increases the cost and makes the circuits error-prone.

It is an object of the present invention to design an evaluation circuit, system and method of the kind mentioned at the outset in a way that enables a reliable and cost-effective differential evaluation of capacitive or inductive sensors, It is to develop further.

According to the invention, said object is realized by the features of claim 1. Thus, the evaluation circuit comprises a first measurement connection designed to connect with the first sensor element of the sensor, and a first measurement connection designed to connect with the second sensor element or reference element of the sensor. A second measurement connection and a charge/discharge circuit designed to output a first charge/discharge signal to the first measurement connection and a second charge/discharge signal to the second measurement connection. And a comparator circuit for comparing the temporal behavior of the first charge/discharge signal with the temporal behavior of the second charge/discharge signal, and a voltage at the output of the comparator circuit connected to the output of the comparator circuit. An integrator circuit having an output voltage that changes according to, wherein the output voltage of the integrator circuit is connected to the first measurement connection for adjusting the first charge/discharge signal, or Connected to the second measurement connection for adjusting the second charge/discharge signal, the measurement signal at the output of the evaluation circuit is derived from the output voltage of the integrator circuit, as well as the measurement signal. Is a measure of the impedance deviation of the first and second sensor elements or the impedance deviation of the first sensor element and the reference element.

With respect to the system, the above object is achieved by the features of dependent claim 12. The system comprises a first and a second evaluation circuit, in particular an evaluation circuit according to the first aspect of the invention, further comprising a first capacitive or inductive sensor having two sensor elements, And a reference element, the first sensor element of the first sensor is connected to the first measurement connection of the first evaluation circuit, the second sensor element of the first sensor, Connected to the second measurement connection of the first evaluation circuit, the reference element is connected to the second measurement connection of the second evaluation circuit, and the first of the second evaluation circuit The measuring connections of are respectively connected to the first and second measuring connections of the first evaluation circuit via a coupling resistor.

According to the invention, the above object is achieved by the features of the dependent claim 18. Therefore, the method of the present invention comprises the steps of generating first and second charge/discharge signals, repeatedly charging and discharging the first sensor element of the sensor by the first charge/discharge signal, and the sensor. A second sensor element or reference element, the step of repeatedly charging and discharging by the second charge and discharge signal, and the temporal behavior of the first charge and discharge signal and the temporal behavior of the second charge and discharge signal. The step of comparing, the step of changing the output voltage of the integrator circuit according to the result of the comparison of the temporal behavior, and the step of changing the output voltage of the integrator circuit, Or the step of adapting the second charge and discharge signal, the difference between the impedance of the first and second sensor elements, or as a measure of the difference between the impedance of the first sensor element and the reference element, Deriving and outputting a measurement signal from the output voltage of the integrator circuit.

In accordance with the invention, it is first recognized that an (analog) measurement signal can be generated by a relatively simple control loop, said signal being the first of the difference between the two impedances, ie the second sensor element. Forming a measure of the difference in impedance of the first sensor element with respect to the sensor element or the reference element. In this case, it is used that the temporal behavior of the charging/discharging signal applied to the inductor depends on the impedance. In the case of a capacitor, the charging/discharging behavior depends on the size of the capacitor, the higher the capacitance, the slower the capacitor will be charged to the maximum voltage value. Conversely, the lower the capacitance, the slower the capacitor will discharge. The same applies to the coil, where the current through the coil rises faster or slower in the case of a voltage jump, depending on the inductance of the coil. Therefore, a comparison of the temporal behavior of the two inductors in response to the excitation signal provides a measure of the difference between the impedances.

Therefore, according to the invention, the first and second charge/discharge signals are generated by the charge/discharge circuit and output to the measurement connection of the evaluation circuit. The first charge/discharge signal is output to the first measurement connection and the second charge/discharge signal is output to the second measurement connection. The first measurement connection is designed to connect with the first sensor element of the sensor. Either the second sensor element or the reference element of the sensor may be connected to the second measurement connection. The charge and discharge circuit is switched off such that each of the first and second charge and discharge signals has a dependency on the inductor connected to the first and second measurement connections, respectively. .. In practice, this dependency usually consists of the temporal behavior of the affected charge/discharge signal. For example, if a square wave signal forms an excitation signal, the edges of the square wave signal are flattened by the connected impedance. The higher the impedance, the more pronounced the flattening. As a result, the charge/discharge signal changes depending on the connected impedance.

To take advantage of these dependencies, the evaluation circuit comprises a comparator that compares the temporal behavior of the first charge/discharge signal with the temporal behavior of the second charge/discharge signal. Depending on the result of the comparison, the comparator outputs a result signal representing a relative temporal behavior. The resulting signal is usually a binary signal, i.e. the signal can take two levels. In this case, the first level indicates that the first charge/discharge signal rises and/or falls faster than the second charge/discharge signal. Therefore, the second level indicates that the second charge/discharge signal rises and/or falls faster than the first charge/discharge signal. The result signal is then sent to an integrator circuit which integrates the comparison result. Then, a voltage representing the incremental number of the integrator circuit is present at the output of the integrator circuit.

In order to prevent the output voltage from continuing to rise indefinitely, the output voltage is connected to one of the measurement connections. As a result, the charge/discharge signal is superimposed with the DC voltage level, which shifts the charge/discharge signal to a positive or negative voltage depending on the configuration of the circuit. And this shifts the time for the charge and discharge signal to reach a certain level. This allows the result signal from the comparator circuit to change and thus take the second level instead of the first level (or vice versa). As a result, the output voltage will no longer rise. Thus, the voltage at the output of the integrator circuit is a measure of how much the impedances at the first and second measurement connections differ from each other. The evaluation circuit according to the invention is inexpensive and provides good results even when the impedance of the sensor element is very low. Furthermore, the dependence of temperature and cable length can easily be removed if the cables between the measurement connection and the sensor element are of approximately the same length and are routed close together. .. The integrator circuit and the comparator circuit do not require any precision components and can instead be built with standard components, resulting in a cost-effective evaluation circuit.

It should be pointed out that the use of the names "first measuring connection" and "second measuring connection" is merely a role of distinguishing the two measuring connections. The circuit is constructed substantially symmetrically so that which of the inductors (ie the first sensor element, the second sensor element or the reference element) is connected to which measurement connection. It doesn't matter. This is true regardless of whether the evaluation circuit is a single unit or multiple evaluation circuits are interconnected to form a system.

It should also be noted that the reference element may be formed by the most diverse components. In this case, it is essential that the reference element, as opposed to the sensor element, is unaffected by the object to be measured. Furthermore, to simplify the evaluation, the reference element should be of the same classification as the sensor, i.e. if a capacitive sensor is to be evaluated, the reference element is formed by a capacitor. And the reference sensor is to be evaluated, the reference element is formed by an inductor. In this case, it is further advantageous if the reference element has high temperature stability, or if the behavior of the reference element with respect to temperature changes is equal or at least similar to the sensor. This is not essential for the accuracy of the output measurement signal, but the effort involved in processing the measurement signal is not small. It is also advantageous, if not essential, to use precision components for the reference element. The tolerance of the reference element can basically be offset by a calibration measurement. However, by using precision components, calibration measurements can be greatly simplified or even eliminated altogether. Furthermore, the reference element may have a fixed value or may be configured as an adjustable coil or capacitor. In this case, conformance may be implemented using a wide variety of methods known from practice. A manually adjustable reference element may be used, as well as an electronically adjustable reference element.

In a preferred development, the evaluation circuit further comprises an inverting circuit, which is preferably formed by an inverting amplifier. The output voltage of the integrator circuit is the input to this inverting circuit. From this input voltage, the inverting circuit produces an output voltage that represents a mirroring of the input voltage with a reference voltage. For example, if the reference voltage has a value of 2.5 volts and the output voltage of the integrator circuit has a value of 3 volts, the inverting circuit will mirror this value with the reference voltage, ie , The output voltage of the inverting circuit is at the same distance from the reference voltage, but on the “opposite side” of the reference voltage. Then, the output voltage of the inverting circuit has a value of 2 volts in this example. When the output voltage of the integrator circuit rises, the output voltage of the inverting circuit drops and vice versa. The output voltage of the inverting circuit thus changes in the opposite direction with respect to the reference voltage and with respect to the output voltage of the integrator circuit. In the implementation of the inverting circuit as an inverting amplifier using an operational amplifier, this aspect is such that the output voltage of the integrator circuit is input to the inverting input of the operational amplifier, and the reference voltage is applied to the operational amplifier. It can be realized by inputting to the non-inverting input.

The first preferred use of this inverting circuit is to increase the level of the measurement signal. In this case, the measurement signal is tapped by the voltage between the output of the integrator circuit and the output of the inverting circuit. As a result, when the output voltage at the integrator circuit changes, the voltage swing increases to twice its value.

A second preferred use of this inverting circuit is to use the output voltage of the inverting circuit to regulate one of the two charge and discharge signals. If the output voltage of the integrator circuit is connected to the first measurement connection, the output voltage of the inverting circuit is the second measurement to adjust the second charge/discharge signal. It is connected to the connection part. Conversely, when the output voltage of the integrator circuit is connected to the second measurement connection, the output voltage of the inverting circuit is adjusted to the second charge connection to adjust the first charge/discharge signal. Connected to one measuring connection. By this method, the regulation of the charge/discharge signal can be improved.

In order to improve the comparison result of the comparator circuit, the evaluation circuit may have first and second binarization circuits, the first binarization circuit being the first measurement connection. And the second binarization circuit is connected to the second measurement connection. The output voltage of the binarization circuit is then input to the comparator circuit. Preferably, the two binarization circuits are each implemented by a Schmitt trigger circuit. Integrated circuits are available in which two such binary circuits are integrated on a single chip. As a result, the behavior of the two binarization circuits with respect to input capacitance, threshold voltage, delay time, temperature effects, and/or additional features is substantially the same. The first and second binarization circuits thus convert the signals at the first and second measurement connections into binary signals in almost the same way, i.e. at the first or second level. Let us assume that the change between the two levels is a signal that is rapid, typically within a few milliseconds or less. A typical binary signal is, for example, a bipolar square wave signal alternating between a positive first level (eg +5V) and a negative second level (eg -5V), or two positive square wave signals. It is a unipolar rectangular wave signal alternating between levels, between two negative levels, or between positive/negative levels and 0V. A general unipolar rectangular wave signal has a level of +5V or 0V, for example.

In a preferred development, the comparator is formed by a flip-flop. D flip-flops have been shown to be particularly suitable. In the present specification, one of the two charge/discharge signals is input to the clock input, and the other of the two charge/discharge signals is input to the data input. If a binary circuit is used, without loss of generality, the output of the first binary circuit may be connected to the clock input of the D flip-flop and the output of the second binary circuit may be , May be connected to the data input of the D flip-flop. The D flip-flop is mostly edge-triggered and outputs the level present on the data input to the output in case of a rising edge on the clock input. A low level if the temporal behavior of the inductor at the first measurement connection is now faster than the inductor at the second measurement connection, and at a rising edge at the clock input. Are still present in the data input. In this case, therefore, a low level will be present at the non-inverted data output of the D flip-flop. If the time behavior of the inductor at the second measurement connection is faster than the inductor at the first measurement connection, the low level is still at the rising edge at the clock input. Present in the data input. In this case, therefore, a low level will be present at the non-inverted data output of the D flip-flop.

The integrator circuit can basically be implemented in various ways. However, the preferred integrator circuit is implemented as an operational amplifier circuit. Such integrator circuits are known in practice. In the simplest case, the output of the operational amplifier is fed back to the inverting input via a capacitor. The input of the integrator circuit is formed by the inverting input of the operational amplifier, whereby the output signal of the comparator circuit in this development is connected to the inverting input of the operational amplifier.

In a particularly preferred refinement, the non-inverting input of the operational amplifier, which is connected as an integrator circuit, is charged with a voltage other than 0V, particularly preferably with a voltage greater than 0V. By this method, the output voltage of the integrator circuit can be offset. In this case, this voltage at the non-inverting input is preferably generated by a voltage divider from the supply voltage of the evaluation circuit. The offset voltage can be shifted according to the selection of the resistance ratio of the voltage divider. The two resistors of the voltage divider have approximately the same value, whereby the offset voltage is equal to half the supply voltage. The resistors of the voltage divider are preferably precision resistors and have a tolerance of 1% or less.

The evaluation circuit preferably has a clock input to which a clock signal can be input. This clock input may be connected to the charging/discharging circuit and may be used to generate the first and second charging/discharging signals. In this case, in the simplest development, the charge/discharge circuit may be formed by a resistor or an interconnection of resistors. This method makes it possible on the one hand to generate a periodic charging/discharging signal, and on the other hand it is also possible to ensure that said charging/discharging signal remains influenced by the inductor connected to said measuring connection. ..

In the first embodiment, the clock signal may be formed by an external clock circuit, preferably by an external oscillator, ie by a clock circuit which does not form part of said evaluation circuit. In a second and preferred development, the evaluation circuit comprises a clock circuit whose output is connected to the clock input of the evaluation circuit. The clock circuit may be formed by a simple oscillator. If both charge and discharge signals are derived from a common clock signal, then no special requirements regarding clock stability need be applied to the oscillator, as it is true for any inductor connected to the measurement connection. , And are affected by the same variations in frequency and/or by the same jitter, and thus the errors cancel out.

Basically, the evaluation circuit according to the invention may be used as a single unit for evaluating a sensor element with respect to another sensor element or with respect to a reference element. However, a particular effect occurs when a plurality of evaluation circuits are interconnected to form a system for evaluating capacitive or inductive sensors.

Such a system according to the invention comprises a first evaluation circuit, a second evaluation circuit, a first capacitive or inductive sensor and a reference element. Basically, it is envisaged that the first and second evaluation circuits are formed by relatively arbitrary evaluation circuits known from the prior art. However, the system works particularly well if the two evaluation circuits are formed by an evaluation circuit according to the invention. The evaluation circuits each have a first and a second measuring connection. The first sensor element of the first sensor is connected to the first measurement connection of the first evaluation circuit, the second sensor element of the first sensor is the first evaluation circuit. Connected to the second measuring connection of The reference element is connected to the second measurement connection of the second evaluation unit. The first measurement connection of the second evaluation unit is used to couple the two evaluation units together. The first measurement connection of the second evaluation unit is connected to the first measurement connection of the first evaluation unit by a first coupling resistor and the first measurement connection of a second coupling resistor. Connected to the second measurement connection of the evaluation unit. By this method, the change in impedance of the first and second sensor elements of the first sensor is added to the measurement signal of the second evaluation circuit as well as the measurement signal of the first evaluation circuit. Influence on. The measurement signal of the first evaluation circuit thus represents the difference between the impedances of the first and second sensor elements of the first sensor, while the measurement signal of the second evaluation circuit is The difference between both sensor elements with respect to the reference element is shown. For example, if the sensor is a capacitance distance sensor with two electrodes, the measurement signal of the first evaluation circuit represents the position of the measuring object with respect to the two sensor elements (the electrodes). The farther the measurement object moves from the center position between the two electrodes, the further the measurement signal moves from the center position, which is exemplified by a voltage of 0 volt. On the other hand, the measurement signal of the second evaluation circuit indicates the magnitude of the influence of the measurement object on both electrodes. If the measuring object and/or its electrical properties are known, the distance of the measuring object to the electrodes can therefore be estimated from the second measuring signal.

In a further development of this system according to the invention, said system further comprises a third evaluation circuit and a second capacitive or inductive sensor. The third evaluation circuit is preferably formed by the evaluation circuit according to the present invention. The second sensor is preferably of the same classification as the first sensor, i.e. if the first sensor is a capacitance sensor, the second sensor is also a capacitance sensor, If the first sensor is formed by an inductive sensor, the second sensor is also an inductive sensor. The first measurement connection of the third evaluation circuit is connected to the first sensor element of the second sensor, the second measurement connection of the third evaluation circuit is the second sensor. Connected to the second sensor element of. The first measurement connection of the third evaluation circuit is further connected to the first measurement connection of the second evaluation circuit by a third coupling resistor, the third evaluation circuit of the third evaluation circuit. The second measurement connection is connected to the first measurement connection of the second evaluation circuit by a fourth coupling resistor. By this method, the third evaluation circuit is further coupled to the second evaluation circuit. In this system, the measurement signal of the first evaluation circuit then additionally represents the difference between the impedances of the two sensor elements of the first sensor. The measurement signal of the third evaluation circuit represents the difference between the impedances of the two sensor elements of the second sensor. The measurement signal of the second evaluation circuit represents the difference between the impedances of all four sensor elements and the reference element.

In a preferred development of a system with two sensors, the sensor element of the first sensor and the sensor element of the second sensor are each constructed symmetrically with respect to each other. The symmetry preferably takes the form of axial symmetry. Particularly preferably, the axis of symmetry of the sensor element of the first sensor is arranged perpendicular to the axis of symmetry of the sensor element of the second sensor.

In the evaluation of capacitive sensors, in a system with two sensors, the individual sensor elements, ie the electrodes of said sensor, are preferably formed by an arc or part of a circle. The arcs of the individual sensor elements preferably form a circular line with four breaks, or a circular area divided into four parts.

In a combination of both developments, i.e., a sensor element having a perpendicular axis of symmetry and a part of an arc or circle as the sensor element of the two sensors, four identically designed arc or circle parts result, The electrodes of the two sensors are in each case arranged alternately. This development of electrodes offers further advantages. The system forms a 3D sensor system, wherein the measurement signals of the first and third evaluation circuits represent the position deviation of the measuring object from the center of the circle, while the measurement signals of the second evaluation circuit are The measurement signal represents the distance of the measuring object on a plane parallel to the electrodes. In this case, the measurement signal of the first evaluation circuit reflects the positional deviation of the second sensor in the symmetry axis direction, and the measurement signal of the second evaluation circuit is the symmetry of the first sensor. It reflects the positional deviation of the measuring object in the axial direction. Therefore, the position and/or the change of the position of the measurement object can be detected in three dimensions.

Such a sensor system can be used in various ways. Therefore, it is envisaged to use this sensor system as a three-dimensional input device. The user can move the object held in the central position from the three-dimensional central position, by doing so, for example by means of a spring, and by doing so specify the orientation in the three dimensions. This can be used, for example, in a virtual reality system. However, it is also envisaged to use the sensor system in a production environment, for example for checking the position of production parts in a work process. Another application scenario may be that the position of the measured object needs to be maintained and that the sensor system needs to determine the deviation from the desired position. From these few examples it is already clear how versatile this sensor system can be used. A person skilled in the art can easily recognize what further application scenarios will occur for the system.

For the synchronization of the individual evaluation circuits, the system preferably has a clock circuit, which is preferably formed by an oscillator. The clock signal generated by the clock circuit is then input to the clock input of the corresponding evaluation circuit. This method ensures that the individual charge and discharge signals can be set correctly in a time relationship to each other. In this case, such a clock circuit may be formed by an external circuit, i.e. by a clock circuit which is not part of one of the evaluation circuits. However, in a preferred development, the clock circuit forms part of one of the evaluation circuits. The clock output of this clock circuit is then connected to the clock input of each evaluation circuit and also to the evaluation circuit including the clock circuit. Basically, in this development it is envisaged that only one of the evaluation circuits comprises a clock circuit. However, each of the evaluation circuits preferably has a clock circuit, in this case one of the clock circuits, since the clock circuit consists of very few elements and therefore only a small additional cost. Only one is activated. This allows the evaluation circuit to be used for general purposes.

In the course of operation of the evaluation circuit according to the invention, the following steps are carried out. Generating first and second charge/discharge signals, first sensor element of the sensor, repeatedly charging/discharging by the first charge/discharge signal, second sensor element of the sensor or reference The element, the step of repeatedly charging and discharging by the second charge and discharge signal, the step of comparing the temporal behavior of the first charge and discharge signal with the temporal behavior of the second charge and discharge signal, the temporal Changing the output voltage of the integrator according to the result of the comparison of the behavior, and adjusting the first charge/discharge signal or the second charge/discharge signal according to the output voltage of the integrator. And deriving a measurement signal from the output voltage of the integrator as a measure of the difference between the impedance of the first and second sensor elements or the impedance of the first sensor element and the reference element. And outputting.

It is understood that these steps may also be performed if the evaluation circuit comprises an inverting circuit or is part of a system according to the invention.

There are various options for advantageously designing and developing the techniques of the present invention. In this regard, with the aid of the drawings, reference is made, on the one hand, to the claims subordinate to the dependent claims, and on the other hand to the following description of preferred exemplary embodiments of the invention. General preferred designs and developments of the present teachings will also be described in connection with the description of the preferred exemplary embodiments of the present invention with reference to the drawings. The drawings show:

FIG. 6 is a circuit diagram of an exemplary embodiment of an evaluation circuit according to the present invention. 2 is a block for a block diagram representing the evaluation circuit of the invention according to FIG. 1. 1 is a first exemplary embodiment of a system according to the invention having three evaluation circuits and two sensors in which the sensor elements are arranged in a circular path. 3 is a second exemplary embodiment of a system according to the invention having three evaluation circuits and two sensors, the sensor elements of which are formed by a part of a circle.

FIG. 1 shows a circuit diagram of an exemplary embodiment of an evaluation circuit according to the invention. It should be explicitly pointed out that any resistor or capacitor values used here, as well as the placement of the individual circuit elements, should be regarded as merely exemplary sizing and construction of the evaluation circuit. Is. One of ordinary skill in the art will be able to make any adaptations and recognize what effect these adjustments have.

The evaluation circuit according to FIG. 1 has a first measurement connection A and a second measurement connection B, to which one of the two sensor elements of the sensor can be connected. .. If the sensor is an inductive sensor, the two sensor elements are formed by the coil of the sensor. In a capacitive sensor, the two sensor elements are formed by the measuring electrodes of the sensor. The measuring connections A, B are connected in this simple case to a charging/discharging circuit 2 formed only by resistors R9 and R10. The connections of the resistors R9, R10 opposite the measurement connections A, B are connected together to the clock input T. In this exemplary embodiment, the clock signal generated by the clock circuit 3 and output at the clock output G is input to this clock input T. The clock circuit 3 comprises a simple oscillator composed of an inverting Schmitt trigger IC 3A, a capacitor C2, and a resistor R12.

The first measurement connection A is further connected to the first binarization circuit 4, and the second measurement connection B is connected to the second binarization circuit 5. The two binarization circuits 4, 5 are in each case implemented by means of inverted Schmitt triggers IC1A and IC1B and the fact that the first part of their names is the same sign means that the two Schmitt triggers are 1 It is intended to indicate being integrated together on one chip. At the same time, this also means that the two Schmitt triggers behave similarly and, in particular, have approximately the same switching threshold. The outputs of the binarization circuits 4 and 5 are connected to the input of the comparator circuit 6. In the illustrated embodiment, the comparator circuit 6 is implemented by a D flip-flop IC2A, the output of the first binarization circuit 4 is connected to the clock input CLK of the D flip-flop IC2A and the second The output of the binarization circuit 5 is connected to the data input D of the D flip-flop IC2A. The set and reset connections R and S of the D flip-flop IC2A are both grounded. The non-inverting data output Q of the D flip-flop IC2A is connected to a further inverting Schmitt trigger IC3B, the output of the inverting Schmitt trigger is connected to the integrator circuit 7 via a resistor R3. The integrator circuit 7 is implemented by an operational amplifier IC4A, and the output of the operational amplifier is fed back to the inverting input of the operational amplifier IC4A via the capacitor C1. The signal from the inverting Schmitt trigger IC3B is also input to the inverting input of the operational amplifier IC4A via the resistor R3. The non-inverting input of the operational amplifier IC4A consists of two resistors R1 and R2, shown here with the same dimensions, of a voltage divider 8 connected between the supply voltage Ucc of the evaluation circuit 1 and ground. Connected to the center tap. The output of the operational amplifier IC4A simultaneously forms the output of the integrator circuit 7.

The output of the integrator circuit 7 is connected to the input of an inverting circuit 9, which in this development is formed by an operational amplifier IC4B which is connected as an inverting amplifier. The circuit elements of the operational amplifier IC4B are precision resistors and are formed by resistors R5 and R7 which set the amplification of -1. The non-inverting input of the operational amplifier IC4B is also connected to the center tap of the voltage divider 8. The output of the operational amplifier IC4B simultaneously forms the output of the inverting circuit 9.

The output of the integrator circuit 7 and the output of the inverting circuit 9 are connected to the measured output 10 of the evaluation circuit 1 via resistors R4 and R6. The pins of the measurement output 10 are labeled D1 and D2. The resistors R4 and R6 essentially serve to limit the current and are therefore protective resistors.

The output of the integrator circuit 7 is connected to the second measurement connection B via a resistor R11. The output of the inverting circuit 9 is connected to the first measurement connection A via a resistor R8.

In addition, the evaluation circuit 1 has a ground connection M which provides a connection to ground. In addition, there are capacitors C3 and C4, which serve to stabilize the supply voltage Ucc.

When the evaluation circuit 1 is operating, the clock circuit 3 generates a rectangular wave signal input to the charge/discharge circuit 2 at the clock input T. This produces first and second charge and discharge signals which are output to the first sensor element, the second sensor element, or the reference element via the first and second measurement connections. In each case, an inductor (not shown here) externally connected to the first or second measuring connection causes a change in the temporal behavior of the respective charge/discharge signal. The first and second charging/discharging signals thus affected vary between the first and second levels via the first and second binarization circuits 4, 5, respectively. Is converted into a rectangular wave signal. The rectangular wave signal output in each case reflects the point in time when the charge/discharge signal exceeds a first threshold value or falls below a second threshold value. Since an inversion Schmitt trigger is used, the rising edge of the rectangular wave signal means that the charge/discharge signal is below the second threshold, while the falling edge of the rectangular wave signal is the first edge. The time point at which the input charging/discharging signal exceeds the threshold value of is indicated.

The rectangular wave signal generated by the first and second binarization circuits causes the D flip-flop IC2A to behave as follows, and the binarization circuit is formed by an inverting Schmitt trigger. , And because the D flip-flop responds to a rising edge at the clock input CLK, the discharge branches of the inductor at the measurement connections A and B are evaluated by the comparator circuit. .. If the inductor externally connected to the measuring connection A is discharged below the threshold and faster than the inductor of the measuring connection B, the level of the output signal of the first binarization circuit 4 Changes to a high level and the level at the output of the second binarization circuit 5 remains low. By this method, a low level is connected to the non-inverting output Q of the D flip-flop if it is a rising edge on the clock input CLK. If the inductor externally connected to the measurement connection B is discharged below the threshold and faster than the inductor of the measurement connection A, the output signal of the second binarization circuit 5 Changes to a high level and the level at the output of the first binarization circuit 4 remains low. If an inductor externally connected to the measurement connection A is also discharged below the threshold value, a rising edge is generated at the output of the first binarization circuit 4, whereby the data input D The high level at is connected to the non-inverted data output Q. The low level at the data output Q of the flip-flop IC2A is therefore faster for the inductor externally connected to the measurement connection A than the inductor externally connected to the measurement connection B. A high level, on the other hand, indicates that the inductor externally connected to the measuring connection B is discharged faster.

A high level is present at the input of the integrator circuit 7 when the inductor externally connected to the measurement connection A is discharged faster by the inverting Schmitt trigger IC 3B. A low level is present when the inductor externally connected to the measuring connection B discharges faster. In the discharged state of the capacitor C1, half of the supply voltage Ucc is present at the output of the integrator circuit 7, due to the voltage at the non-inverting input of the operational amplifier IC4A. The behavior of the integrator circuit 7 now depends on what the output voltage of the inverting Schmitt trigger IC 3B looks like. In the simplest case, a voltage varying between a positive voltage (usually Ucc) and 0V is output by the inverting Schmitt trigger. By applying a voltage of Ucc/2 at the non-inverting input of the operational amplifier IC4A and by connecting the operational amplifier IC4A as an inverting integrator, the positive voltage at the input of the integrator circuit 7 is , Reducing the voltage at the output of the integrator circuit. Conversely, when a level of 0V is applied to the input of the integrator circuit 7, the voltage at the output of the integrator circuit rises. A faster discharge at the measurement connection A thus lowers the output voltage of the integrator, while a faster discharge at the measurement connection B raises the output voltage of the integrator.

FIG. 2 shows the symbols of the blocks used in the subsequent block diagram as a summary of the evaluation circuit according to FIG. On the left side, the evaluation circuit 1 has first and second measurement connections A, B and a ground connection M. The clock input T, the clock output G and the input Ucc for the supply voltage are shown on the upper side. The poles D1 and D2, which together form the measurement output 10, are shown on the right. The ground connection GND is shown on the lower side.

This summary of the evaluation circuit is used in the block diagrams of FIGS. 3 and 4, which represent two exemplary embodiments of a system according to the invention. The exemplary embodiment according to FIG. 3 comprises first, second and third evaluation circuits 11, 12, 13 as well as first and second sensors 14, 15 and a reference element 16. The electrodes/sensor elements A1 and B1 of the first sensor 14 are axially symmetric with respect to a horizontal line. The same applies to the sensor elements A2, B2 of the second sensor 15, which are axisymmetric with respect to the vertical. These two axes of symmetry are at right angles to each other. In addition, the four sensor elements A1, A2, B1, and B2 are located on a common circular line, and the sensor element of one sensor is always arranged alternately with the sensor element of the other sensor. I also understand.

The first measurement connection A1 of the first evaluation circuit 11 is connected to the first sensor element A1 of the first sensor 14. The second measurement connection B1 of the first evaluation circuit 11 is connected to the second sensor element B1 of the first sensor 14. The first measurement connection A2 of the third evaluation circuit 13 is connected to the first sensor element A2 of the second sensor 15. The second measurement connection B2 of the third evaluation circuit 13 is connected to the second sensor element B2 of the second sensor 15. The second measurement connection B3 of the second evaluation circuit 12 is connected to the reference element 16. The first measurement connection A3 is connected via the first coupling resistor RA1 to the first measurement connection A1 of the first evaluation circuit 11 via the second coupling resistor RB1. To the second measurement connection B1 of the first evaluation circuit 11 via the third coupling resistor RA2 to the first measurement connection A2 of the third evaluation circuit 13 and to the fourth It is connected to the second measuring connection B2 of the third evaluation circuit 13 via a coupling resistor RB2. The ground connections M of the three evaluation circuits 11, 12, 13 are connected to each other and to the ground electrode of the reference element. The clock circuit of the second evaluation circuit 12 is active, so that the clock output G of the second evaluation circuit 12 is connected to the clock input T of all three evaluation circuits 11, 12, 13. Has been done. In this way, the charge and discharge signals are synchronized at all measurement connections.

During operation of this system, a measurement signal that depends on the impedance difference between the sensor elements A1, B1 of the first sensor 14 is accessible between the poles D1 and D2 of the first evaluation circuit. This measurement signal thus indicates the distance that the measurement object has moved vertically from the center position (the center point of the circle in which the sensor element is located). The measurement signal, which depends on the impedance difference between the sensor elements A2, B2 of the second sensor 15, is accessible between the poles D3 and D4 of the third evaluation circuit. This measurement signal thus indicates the distance that the measurement object has moved horizontally from said central position. The measurement signal, which depends on the impedance difference of all four sensor elements A1, A2, B1, B2 with respect to the reference element 16, is accessible between the poles D5, D6 of the second evaluation circuit. This measurement signal is a measure of the distance of the measured object perpendicular to the plane of the drawing. The measured object should be small relative to the sensor, ie the cross-sectional area of the measured object is smaller than the diameter of the sensor in the direction of the sensor. The object to be measured may be, for example, a ball or a cylindrical rod whose end face is directed toward the sensor.

It will be readily appreciated that the system shown works well even in the presence of only the first sensor, the first and second evaluation units and the reference element. In this case, the position detection capability is limited to the horizontal or vertical direction in the plane of the drawing and the direction perpendicular to the plane of the drawing.

The exemplary embodiment of the system according to the invention shown in FIG. 4 is similar to the exemplary embodiment of FIG. 3, in which the sensor element is formed by a part of a circular surface rather than an arc. The other operation modes are almost the same.

Regarding other advantageous embodiments of the teaching according to the invention, reference is also made to the general part of the specification and the appended claims in order to avoid repetition.

Finally, it is clear that the exemplary embodiments described above serve only to explain the claimed teachings and are not intended to limit the claimed teachings to the exemplary embodiments. Be pointed out.

1 Evaluation Circuit 2 Charging/Discharging Circuit 3 Clock Circuit 4 First Binaryization Circuit 5 Second Binaryization Circuit 6 Comparator Circuit 7 Integrator Circuit 8 Voltage Divider 9 Inversion Circuit 10 Measured Output 11 First Evaluation Circuit 12 Second Evaluation circuit 13 Third evaluation circuit 14 First sensor 15 Second sensor 16 Reference element

Claims (18)

An evaluation circuit for evaluating a capacitance sensor or an inductive sensor,
A first measuring connection (A) designed to connect with a first sensor element of a sensor (14, 15), and a second sensor element or reference element (16) of said sensor (14, 15) A second measurement connection (B) designed to connect with
A charging/discharging circuit designed to output a first charging/discharging signal to the first measurement connection (A) and a second charging/discharging signal to the second measurement connection (B) ( 2) and
A comparator circuit (6) for comparing the temporal behavior of the first charge/discharge signal with the temporal behavior of the second charge/discharge signal;
An integrator circuit (7) connected to the output of the comparator circuit (6), the output voltage of which changes according to the voltage at the output of the comparator circuit (6);
Equipped with
The output voltage of the integrator circuit (7) is connected to the first measurement connection (A) to adjust the first charge/discharge signal or adjusts the second charge/discharge signal. To the second measuring connection (B) for
The measurement signal at the output (10) of the evaluation circuit (1) is derived from the output voltage of the integrator circuit (7), and the measurement signal is of the impedance of the first and second sensor elements. An evaluation circuit, which is a measure of the difference or the impedance difference between the first sensor element and the reference element. An inverting circuit (9), preferably an inverting amplifier, wherein the output voltage of the integrator circuit (7) is input to the input of the inverting circuit and the inverting circuit (9) with respect to a reference voltage (Ucc/2). 2. The evaluation circuit according to claim 1, wherein the output voltage of the switch changes in the opposite direction to the output voltage of the integrator circuit (7). 3. The evaluation circuit according to claim 1, wherein the measuring signal is formed by a voltage between the output voltage of the integrator circuit (7) and the output voltage of the inverting circuit (9). The output voltage of the inverting circuit (9) regulates the first charge/discharge signal when the output voltage of the integrator circuit (7) is connected to the second measurement connection (B). In order to be connected to the first measurement connection (A) or the output voltage of the integrator circuit (7) is connected to the first measurement connection (B) Evaluation circuit according to claim 1 and claim 2 or claim 3, characterized in that it is connected to the second measuring connection (B) in order to adjust the charging/discharging signal of the. The first measurement connection (A) is connected to a first binary conversion circuit (4) and the second measurement connection (B) is connected to a second binary conversion circuit (5). The first and second binarization circuits (4,5) are each preferably characterized in that they are each preferably implemented by a Schmitt trigger circuit. Evaluation circuit. 6. The comparator circuit (6) according to any one of claims 1 to 5, characterized in that it comprises a D flip-flop (IC2A) having a clock input (CLK) and a data input (D). Evaluation circuit. The output of the first binarization circuit (4) is connected to the clock input (CLK) of the D flip-flop (IC2A), and the output of the second binarization circuit (5) is the D flip-flop. 7. Evaluation circuit according to claim 5 and claim 6, characterized in that it is connected to the data input (D) of (IC2A). Evaluation circuit according to any one of claims 1 to 7, characterized in that the integrator circuit (7) is implemented by an operational amplifier (IC4A). The non-inverting input of the operational amplifier (IC4A) is connected to a voltage that is above zero volts, which voltage is preferably above zero volts, preferably via a voltage divider (8) in the evaluation circuit. Evaluation circuit according to claim 5, derived from the supply voltage (Ucc) of (1). Characterized by a clock input (T), said clock input (T) being connected to said charging/discharging circuit (2), said charging/discharging circuit (2) from said signal present at said clock input (T) Designed to induce one and a second charge/discharge signal, said charge/discharge circuit (2) preferably being formed by an interconnection of one resistor or a plurality of resistors (R9, R10), The evaluation circuit according to any one of claims 1 to 9. Evaluation circuit according to claim 10, characterized by a clock circuit (3), the output (G) of the clock circuit (3) being connected to the clock input (T). A system for evaluating a capacitive sensor or an inductive sensor, comprising:
A first evaluation circuit (11), in particular an evaluation circuit according to any one of claims 1 to 11,
A second evaluation circuit (12), in particular an evaluation circuit according to any one of claims 1 to 11,
A first capacitive or inductive sensor (14) having two sensor elements, and a reference element (16),
Equipped with
The first sensor element of the first sensor (14) is connected to the first measurement connection (A1) of the first evaluation circuit (11) and the first sensor (14) of the first sensor (14) is connected. The second sensor element is connected to the second measurement connection (B1) of the first evaluation circuit (11),
The reference element (16) is connected to the second measurement connection (B3) of the second evaluation circuit (12),
The first measurement connection (A3) of the second evaluation circuit (12) is connected to the first and second measurement circuits (11) of the first evaluation circuit (11) via coupling resistors (RA1, RB1), respectively. System connected to a second measurement connection (A1, B1). A third evaluation circuit (13), in particular an evaluation circuit according to any one of claims 1 to 11, and a second capacitance sensor or inductive sensor (15) having two sensor elements. Characteristically, the first sensor element of the second sensor (15) is connected to the first measurement connection (A2) of the third evaluation circuit (13) and the second sensor (15) ) Said second sensor element is connected to a second measurement connection (B2) of said third evaluation circuit (13) and said first measurement connection of said second evaluation circuit (12). (A3) is further connected to the first and second measurement connections (A2, B2) of the third evaluation circuit (13) via coupling resistors (RA2, RB2), respectively. The system according to claim 12. The sensor element of the first sensor (14) and the sensor element of the second sensor (15) are each constructed symmetrically, and the axis of symmetry of the first sensor (14) and System according to claim 13, wherein the axes of symmetry of the second sensors (15) are preferably arranged at right angles to each other. 15. The sensor element of the first sensor (14) and the sensor element of the second sensor (15) are formed by an arc or by a part of a circle. The system described in. 16. A clock circuit, characterized in that the clock signal generated by said clock circuit is input to the clock input (T) of each said evaluation circuit (11, 12, 13). The system according to paragraph 1. One of the evaluation circuits (11, 12, 13) has a clock circuit (3) and outputs the clock signal generated by the clock circuit (3) via a clock output (G). According to claim 12, characterized in that the clock output (G) is connected to the clock input (T) of the further evaluation circuit (11, 12, 13) of the system. The system according to claim 15. A method for evaluating a capacitance sensor or an inductive sensor, in particular a method for evaluating using the evaluation circuit according to any one of claims 1 to 11.
Generating first and second charge and discharge signals,
Repeatedly charging and discharging the first sensor element of the sensor (14, 15) with the first charge and discharge signal;
Repeatedly charging and discharging the second sensor element or reference element (16) of the sensor (14, 15) with the second charge/discharge signal;
Comparing the temporal behavior of the first charge and discharge signal with the temporal behavior of the second charge and discharge signal;
Changing the output voltage of the integrator circuit (7) according to the result of the comparison of the temporal behavior;
Adjusting the first charge/discharge signal and/or the second charge/discharge signal according to the output voltage of the integrator circuit (7);
A measurement signal from the output voltage of the integrator circuit (7) is used as a measure of the difference between the impedances of the first and second sensor elements or the impedance of the first sensor element and the reference element. Guiding and outputting.

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